He will be ordered to stand trial and cannot leave the country, although he will not be physically detained, the agency said.

When previously questioned by prosecutors, Mr Won reportedly denied the charges against him.

Kim Yong-pan, the former head of Seoul's police, will also be indicted, prosecutors say. He is suspected of obstructing a police investigation into the matter.

In April, police announced that at least two NIS agents appeared to have posted political comments on the internet, although they could not determine whether the agents were part of a larger operation.

However, prosecutors now say they have proof that the NIS posted comments online using more than 100 identities.